1. Field of the Invention
The present invention relates to an optical connector which comprises a ferrule and a connection mechanism which is integrated with the ferrule, in which an internal optical fiber is embedded in the ferrule and end face grinding is performed in the ferrule, and the optical connector butt connects the internal optical fiber and an insert optical fiber within a positioning groove which is provided in the connection mechanism.
2. Description of the Related Art
Generally, an end face grinding of a ferrule is performed in an optical connector in order to reduce connection loss in optical connector connection.
In this case, in order to suppress an optical loss caused by Fresnel reflection, generally, a refraction index adjusting agent is interposed in a gap (space) generated between the ferrule end faces (between optical fiber end faces).
Furthermore, it is common practice that the optical fiber end face be obliquely (bevel) ground by obliquely grinding the ferrule end face, such that the Fresnel reflection is eliminated as much as possible.
Furthermore, the following method is performed, in which the optical fiber end face is spherically ground by spherically grinding the ferrule end face, such that a physical contact (PC connection) in which the optical fiber end faces are directly contacted to each other without a gap.
Furthermore, as a device for obtaining a large return loss (a device for suppressing a reflection) in an optical connector connection, an optical fiber connector is shown in Patent Document 1 (Optical Connector and Manufacturing Method Thereof; Japanese Unexamined Patent Application, First Publication No. H05-181040 (FIG. 1, claims 1 and 3, Paragraph [0023])), in which a core end face of the optical fiber is formed in a hemispherical shape with a necessary protruded amount, by etching the mutually butting end faces of the optical fibers with a particular etching solution (an etching solution in which the higher the core dopant concentration of the optical fiber, the lower the etching speed).
A large return loss is obtained, since the cores are directly contacted to each other (physical contact) by forming the optical fiber core to a protruded hemispherical shape.
Furthermore, as the same device for obtaining a large return loss in an optical connector connection, an optical connector is shown in Patent Document 2 (Optical Connector; Japanese Unexamined Patent Application, First Publication No. H06-174971 (FIGS. 1 and 3, claims 1 and 2, Paragraphs [0027] and [0028])), in which the optical connector is configured in such a way that the optical fibers are not contacted and detached from each other when the ferrules are contacted without pressing, and the optical fibers are contacted to each other when a pressure is applied. In this case, the gap between the optical fibers when the ferrules are contacted without pressing is set to be within a deformation volume of the ferrule which is determined by the pressure when the ferrule is pressed within the elastic limit of the ferrule. That is, the retract amount d of the optical fiber end face with respect to the ferrule end face is set to an appropriate value which corresponds to the elastic coefficient of the ferrule.
As shown in FIG. 1, in an optical connector 1, a connection mechanism 4 is integrated with a ferrule 3 to which an internal optical fiber 2 is embedded and an end face grinding is performed, and the internal optical fiber 2 and an insert optical fiber 10a inserted from outside is but connected within a positioning groove provided in the connection mechanism 4. The optical connector 1 can be easily assembled without a grinding operation in the field. Therefore, the optical connector 1 is widely used as a field assembly type optical connector.
The connection mechanism 4 includes a base 6 which is integrated with the ferrule 3 and a positioning groove 5a which connects to an optical fiber hole 3a of the ferrule is formed thereon, lids 7, 8 which are disposed opposite to the base 6, and a plate spring 9 which elastically clamping both of them. As shown in FIG. 4, each lid 7, 8 is openable and closable with respect to the base 6 via a wedge shape opening and closing member 11. When assembling the optical connector 1, the lids 7, 8 are put in a slightly opened state, and the insert optical fiber 10a is inserted into the positioning groove 5a and butts to the internal optical fiber 2.
The appearance of the optical connector 1 shown in FIG. 1 and the configuration shown in FIG. 4 are common to both the present invention and the related art. In this kind of optical connector 1, generally, optical fibers with an orthogonal end face are butt connected via a refraction index adjusting agent in a butting portion of an internal optical fiber within a positioning groove and an insert optical fiber (FIGS. 4 to 6 of Patent Document 3, “Optical Connector”; Japanese Unexamined Patent Application, First Publication No. H08-201652).
Furthermore, in an optical attenuation element not in an optical connector, there is a configuration in which optical fibers are inserted from right and left into a micro through-hole opened in the center of a columnar shape ferrule, such that a gap is formed between tip end faces of the optical fibers, and the tip end faces of two optical fibers are obliquely ground (FIG. 1, claims 1 and 3, Paragraph [0024]. in Patent Document 4, “Optical Attenuation Element and Manufacturing Method Thereof”; Japanese Unexamined Patent Application, First Publication No. H05-100117).
In this optical attenuation element, reflected return light can be reduced by beveling the end face of the optical fiber opposite to the micro through-hole. The bevel angle of the optical fiber end face in the optical attenuation element is 8 degrees or more with respect to an orthogonal face of an optical axis.
As described above, generally, in an optical connector having a configuration as shown in FIG. 1 in which an internal optical fiber and an insert optical fiber are butt connected within a positioning groove, merely the optical fibers with an orthogonal end face are mutually butt connected via a refraction index adjusting agent. In this case, not only a suppression of the reflection from the refraction index adjusting agent is desirable, but also the achievement of a low reflecting connection. In addition, assembling of the optical connector will be simplified if the refraction index adjusting agent is no longer required.
In this case, under a constraint where a reflection suppression unit in a butting portion (ferrule end face) of the optical connectors is not suitable for a butting portion of the optical fibers within a positioning groove, it is desirable to realize a reflecting connection with a simple method without a complicated configuration.
For example, the method of Patent Document 1 etches the optical fiber, and is complicated.
Furthermore, the method of Patent Document 2 needs to be exactly set the retract amount d of an optical fiber end face with respect to the ferrule end face. However, the retract amount d of an optical fiber end face needs to be set exactly corresponding to the elasticity of the ferrule. Therefore, the method of Patent Document 2 is also complicated.
Furthermore, Patent Document 3 relates to an optical attenuator, and a gap is formed between the optical fibers. Therefore, Patent Document 3 differs from an optical connector in which the optical fibers are mutually butt connected.
Thereupon, a method is being focused on, in which a reflection in a butting portion is suppressed by beveling each end face of the internal optical fiber and the insert optical fiber in an optical connector having a configuration as shown in FIG. 1.
In this case, polishing an end face of an optical fiber to a beveled end face is also complicated. Therefore, cutting an end face of an optical fiber to a beveled end face is being focused.
However, when inserting an insert optical fiber 10a into a positioning groove 5a and butt connecting the insert optical fiber 10a to an internal optical fiber 2 during the assembly of an optical connector, since the tip ends of the beveled end faces of both the optical fibers 2, 10a are sharp, there is a possibility that the optical fibers 2, 10a will become chipped when butt connecting the insert optical fiber 10a to the internal optical fiber 2 within an invisible positioning groove. Since the optical connector with a chipped end face portion of an optical fiber is a defective product, it is important to avoid chipping the tip end portion while butting.